Method for producing a luminophore or fluorescent layer

ABSTRACT

A method for producing a coating of fluorescent or luminophore material includes the steps of depositing the luminophore material from a vapor phase on a substrate in such a manner that at least 30 weight-% of the luminophore material used is deposited on the substrate and then abrading or polishing the luminophore coating to a predetermined even layer thickness utilizing a polishing agent.

BACKGROUND OF THE INVENTION

The invention is directed to a method for producing a luminophore layer.

DE 195 16 450 C1 discloses a method for producing a luminiferous layercomposed of CsI:Tl. It is thereby provided that the pressure in thevapor-deposition system is higher than the vapor pressure of thethallium iodide, at least during the vapor-deposition. A luminophorelayer whose light yield is improved can be produced based on thismethod.

An experimental method for producing a luminophore layer composed ofCsI(Na) is also known from “preparation of Self-Supporting Large-AreaPolycrystalline Structures of CsI(Na) by Evaporation”, W. Schubert,Siemens Forsch.- und Entwickl.-Ber., Vol. 3 (1974), No. 2, SpringerVerlag, 1974. A vapor-deposition rate of 65 weight-% of the utilizedmaterial is thereby achieved.

DE 198 52 326 A1 discloses a method that is particularly suited forcoating a substrate with GaBr-doped luminophores. The luminophore isthereby placed onto a heated evaporation source in a vacuum in thevapor-deposition chamber, said luminophore immediately vaporizingthereat and depositing on the substrate.

DE 44 29 013 A1 discloses an apparatus for the vapor-deposition of asubstrate having an X-ray measuring instrument for measuring the layerthickness. The vapor-deposition rate is regulated dependent on themeasured result of the layer thickness measurement in order to achievean optimally uniform layer thickness.

DE 24 35 629 A1 discloses a method for smoothing the surface of aluminophore layer applied on a substrate. The surface is thereby workedwith forging bodies in the fashion of forging.

DE 28 32 141 A1 discloses a method for manufacturing radiation converterscreens, whereby a luminophore layer applied on a substrate is groundand polished for achieving a uniform layer thickness. Irregularitiesthat project above the luminophore layer are thereby in fact eliminated.However, relatively long-wave irregularities are generated when grindingand polishing. Moreover, relatively large grinding agent grains areworked into the luminophore layer during grinding. These reduce theoptical quality of the luminophore layer.

In order to counter this disadvantage, attempts have already been madein the Prior Art to arrange the luminophore source at as great adistance as possible from the substrate during the vapor-deposition.Luminophore layers deposited in this way are relatively uniform in termsof their layer thickness. However, a great deal of material must beutilized here during the vapor-deposition because only about 10 weight-%of the evaporated material are deposited on the substrate here.

SUMMARY OF THE INVENTION

An object of the invention is to eliminate the disadvantages of thePrior Art. In particular, a method should be specified with which aluminophore layer or fluorescent layer having an optimally uniform layerthickness can be manufactured in an optimally simple way.

This object is achieved by a method for producing a luminophore layercomprising the following steps:

a) depositing of the luminophore from the vapor phase on a substratesuch that the spacing of the luminophore source from the substrate isselected such that at least 30 weight-% of the utilized luminophore aredeposited on the substrate; and

b) abrasively eroding of the luminophore layer to a prescribed, uniformlayer thickness by means of a polishing agent.

The economic feasibility of the method is enhanced in that at least 30weight-% of the utilized luminophore are deposited on the substrate. Auniform layer thickness can then be achieved by means of a following,abrasive erosion of the luminophore layer with a polishing agent.

Expediently, the substrate is rotated during step a). A sponge or feltmanufactured of plastic is advantageously employed as the polishingagent. Powdered luminophore can be contained in the sponge or felt.Expediently, this is the same luminophore that has been deposited on thesubstrate. Doped alkali halides such as, for example, CsI:Na, CsI:Tl orCsBr:Eu particularly come into consideration as the luminophore. Whatthe inclusion of the powdered luminophore in the sponge or felt duringthe abrasive erosion achieves is that fissures in the luminophore layerare filled out with the powdered luminophore.

The abrasive erosion can be implemented by means of a nonaqueous liquid,preferably, ethanol, silicone oil or cyclohexane.

Corundum or diamond particles can be added to the liquid. The rate ofthe erosive abrasion can thus be increased.

According to another design feature, the layer thickness distribution ofthe deposited luminophore layer can be measured topically resolvedbefore step b), and the corresponding data can be stored. For theimplementation of such a topically resolved measurement, the luminophorelayer deposited on the surface of the substrate can be measured with aprobe of a CNC measuring machine or with an optical method such as, forexample, oblique light laser interferometry. Measuring the layerthickness by means of X-ray absorption measurement also comes intoconsideration. A pressing power whose size is inversely proportional tothe measured layer thickness can be applied onto the polishing agent.For example, the pressing power on the polishing agent is increasedwhere the layer thickness is high. Further, the relative speed of thesubstrate relative to the polishing agent can be inversely proportionalto the measured layer thickness. For example, the rotational or,respectively, circumferential speed of the substrate is especially highat locations where the measured layer thickness is low, and it is lowwhere the measured layer thickness is high. The above-described methodfor abrasive erosion is expediently implemented using acomputer-assisted mechanism that uses the measured data. The polishingagent, for example, can be radially moved over the rotating substrate.

An exemplary embodiment of the inventive method is explained in greaterdetail below on the basis of the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a picture of an inhomogeneity in a luminophore layer, whichpicture was made with a scanning electron microscope;

FIG. 2 is a picture of a fracture edge of a luminophore layer through aninhomogeneity, which picture was made with a scanning electronmicroscope; and

FIG. 3 is a picture onto the surface of a luminophore layer, whichpicture was made with a scanning electron microscope.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For producing a luminophore layer for a radiation converter screen, asubstrate manufactured, for example, of a planar aluminum disk isintroduced into a known vapor-deposition system. Such a vapor-depositionsystem is known, for example, from DE 195 16 450 C1, whose disclosure isherewith incorporated. The temperature of the substrate is set such thatthe saturation vapor pressure over the luminophore layer condensing onthe substrate is lower than the vacuum prevailing in thevapor-deposition. A luminophore layer having a thickness ofapproximately 500 μm is vapor-deposited. The spacing between the sourceof the luminophore to be evaporated and the substrate is therebyselected such that at least 30 weight-%, and preferably 50 weight-%, ofthe evaporated luminophore precipitate on the substrate.

In particular, the vapor-deposited luminophore layer comprises thepunctiform inhomogeneities shown in FIGS. 1 and 2, these being caused bya giant grain growth. In addition, a non-uniform layer thicknessdistribution on the substrate caused by the vapor-deposition can occur.

For producing a uniform layer thickness, the luminophore layer isreduced to a prescribed, uniform layer thickness by means of a polishingagent. A felt, preferably a plastic felt, or a polishing agent equippedwith plastic bristles is expediently employed as the polishing agent.The polishing ensues wet, preferably with a non-aqueous liquid, forexample ethanol, silicone oil or cyclohexane. Diamond particles can beadded to the liquid. Luminophore particles can be contained in thepolishing agent in order to fill fissures that may potentially bepresent at the surface of the luminophore layer. To that end, thepolishing agent is expediently placed into a saturated aqueous solutionof the luminophore to be polished and is subsequently dried.

The measurement of the layer thickness of the luminophore layer appliedonto the substrate ensues, for example, with the probe of a CNCmeasuring machine, an optical method such as, for example, oblique lightlaser interferometry or by means of X-ray absorption measurements.

The data acquired in the layer thickness measurement are made availableto a polishing device that works according to the zonal correctionprinciple. Such a polishing device is available, for example, fromJenOptik AG under the name “Feinkorrekturmaschine FK 300”. With such apolishing device, a low circumferential speed of the substrate and—atthe same time—a high pressing power onto the substrate can be set atlocations of the high layer thickness. A higher circumferential speedand a lower pressing power can be set given a low layer thickness. Thecontrol of the circumferential speed, of the pressing power and theradial position of the polishing or grinding agent relative to therotating substrate ensues automatically, preferably it iscomputer-assisted.

The inventive method succeeds in setting the layer thickness of theluminophore layer with a deviation of less than 2%. In the case of aluminophore layer produced, for example, of CsBr:Eu, this corresponds toa maximum layer thickness deviation of less than 10 μm.

Another advantage of the inventive method is that fissures located atthe surface of the luminophore layer, as shown, for example, in FIG. 3,are simultaneously closed by the luminophore particles contained in thepolishing agent.

1. A method for producing a luminophore layer comprising the steps ofdepositing a luminophore from a vapor phase on a substrate, so that atleast 30 weight-% of the utilized luminophore is deposited on thesubstrate; and using a polishing agent to abrasively erode theluminophore layer to a prescribed uniform layer thickness and to fillthe fissures on the luminophore layer.
 2. A method according to claim 1,which includes, prior to abrasively eroding, topically measuring thelayer thickness of the deposited luminophore layer and recording thisdata.
 3. A method according to claim 2, wherein the step of abrasivelyeroding includes applying a pressing power to the polishing agent, whichis inversely proportional to the measured layer thickness.
 4. A methodaccording to claim 2, which includes a relative rotation of thesubstrate to the polishing agent, and adjusting the speed of therelative rotation proportional to the measured layer thickness.
 5. Amethod according to claim 2, wherein the step of abrasively eroding isimplemented by computer-assisted employment of the measured data.
 6. Amethod according to claim 1, wherein the polishing agent is selectedfrom a sponge and felt manufactured of plastic.
 7. A method according toclaim 6, wherein powder luminophore is contained in the polishing agent.8. A method according to claim 1, wherein the abrasive eroding isimplemented by means of a non-aqueous liquid.
 9. A method according toclaim 8, wherein the liquid is selected from a group consisting ofethanol, silicone oil and cyclohexane.
 10. A method according to claim8, wherein the liquid contains particles selected from corundumparticles and diamond particles.
 11. A method for producing aluminophore layer comprising the steps of depositing a luminophore froma vapor phase on a substrate, so that at lest 30 weight % of theutilized luminophore is deposited on the substrate; rotating thesubstrate during the step of depositing; and abrasively eroding theluminophore layer to a prescribed uniform layer thickness by using apolishing agent.
 12. A method according to claim 11, wherein the step ofabrasively eroding utilizes a polishing agent selected from a sponge andfelt manufactured of plastic.
 13. A method according to claim 12,wherein powder luminophores are contained in said polishing agent.
 14. Amethod according to claim 13, wherein the step of abrasively erodingincludes applying a non-aqueous liquid.
 15. A method according to claim14, wherein the non-aqueous liquid is selected from a group consistingof ethanol, silicone oil and cyclohexane.
 16. A method according toclaim 14, wherein particles selected from corundum and diamond particlesare added to the liquid.